Switching regulators are widely used in various electronic devices for sourcing power to the electronic devices from a power source. The electronic device(s) powered by a switching regulator may be referred to as a load of the switching regulator. Generally, the switching regulator may be able to convert a power source voltage into an appropriate output voltage through controlling a switch module coupled to the power source voltage to switch on and off, thereby regulating power transmitted to the load.
The switching regulator generally comprises a control module for controlling the switch module so as to achieve good load regulation (load regulation may refer to change of the output voltage with an output current drawn by the load) based on a feedback signal indicative of the output voltage and a reference signal indicative of a desired value of the output voltage. However, the switch module, the control module and a module for providing the reference signal are generally fabricated on integrated circuit die(s) and encapsulated in a package. All the circuits and modules inside the package may be referred to as internal circuits and may be referenced to an internal reference ground, which is usually connected to a ground pin of the package via a resistive connecting component. During the switch module switching on and off periodically, a relatively large switching current (compared with currents flowing through other internal circuits of the switching regulator) may flow through the resistive component, resulting in an offset voltage from the reference ground to the package ground pin.
The offset voltage may change with the output current drawn by the load. If the output current increases, an average of the offset voltage (average offset voltage) increases as well. If the output current decreases, the average offset voltage also decreases. The reference signal with respect to the ground pin is thus influenced by the offset voltage, more concretely by the output current. Due to the reference signal changing with the output current, the load regulation performance of the switching regulator may decrease. For example, for a step down switching regulator, when the output current drawn by the load increases, the average offset voltage also increases, leading to decrease in the reference signal with respect to the ground pin. The decrease of the reference signal results in a smaller difference between the feedback voltage and the reference signal than should be without the decrease of the reference signal, which adversely worsen the load regulation.
A need therefore exists for solving the problem of influence of the offset voltage to the reference signal and the load regulation of a switching regulator circuit.
One existing solution provides a separate ground pin for the switch module, which is different from the ground pin used for the other circuits and modules of the switching regulator. Thus, the relative large current flowing through the switch module no longer flows through the ground pin used for other circuits and modules including the module for providing the reference signal. Therefore, the reference signal in this case is unaffected by the output current. However, this solution requires an additional ground pin, which increases cost and size of the switching regulator.
Another existing solution lies in reducing the parasitic resistance caused by the resistive connecting component (e.g. bondwire) between the internal reference ground and the package ground pin. This can be accomplished by Chip Scale or flip-chip bonding of the ground pin. However while resistance is reduced it is not insignificant. Moreover Chip Scale or flip-chip bonding connection is relatively expensive in area due to its low mechanical density with respect to a high density bondwire connection.